Lamination of olefin polymer to various substrates

ABSTRACT

Olefin polymers, such as polyethylene, are bonded to various substrates, such as metal, glass, plastic, paper, wood, by surface sulfonating the olefin polymer and adhering the surface sulfonated olefin polymer to the substrate with epoxy resin.

United States Patent 1191 Walles *Dec. 118, 1973 [5 LAMINATION 0F OLEFINPOLYMER T0 3,142,582 7/1964 Koretzky ct a1. 117/47 A VARIOUS SUBSTRATES3,192,092 6/1965 Schonhorn 156/308 I 3,586,569 6/1971 Caiola 1 156/308Inventor: e m dla Mlch- 3,607,350 9/1971 Rathsack... mm A I 3,625,41412/1971 Caiola 156/308 [73] Asslgnee ll Company 3,684,554 8/1972 Donaldet a1. 117/47 A Mldland, 3,686,016 8/1972 Maguire et a1.... 117/47 A 1Notice: The portion of the term of this 3,689,303 9/1972 Maguire et a1 117/47 A patent Subsequent to Dec. 21, 1988, 3,036,930 5/1362 grlmmmgeret al.. 1:7/93 has been disclaimed 3,306,791 2/1 67 ye 56/3 3,725,1094/1973 Schulz et al. 117/47 A [22] Filed: Aug. 11,1971

[2]] Appl' 172385 Primary Examiner-Harold Ansher Related US. ApplicationData Attorney-William M. Yates et a1. [63] Continuation-impart of Ser.No. 764,915, Oct. 3,

1968, Pat. No. 3,629,025.

[52 U.S. c1 156/3, 117/47 A, 156/308, ABSTRACT 156/330 [51] Int. Cl...B32b 31/24, B32b 27/38, B32b 27/32 Olefin polymers, such aspolyethylene, are bonded to [58] Field of Search 156/3, 330, 308;various substrates, such as metal, glass, plastic, paper, 117/47 A wood,by surface sulfonating the olefin polymer and adhering the surfacesulfonated olefin polymer to the [56] References Cited substrate withepoxy resin.

UNlTED STATES PATENTS 3,629,025 12/1971 Walles 156/69 6 Claims, N0Drawings LAMINATION OF OLEFIN POLYMER TO VARIOUS SUBSTRATESCROSS-REFERENCES TO RELATED APPLICATIONS This is a continuation-in-partof Ser. No. 764,915 filed in Oct. 3, l968 now US. Pat. No. 3,629,025.

BACKGROUND OF THE INVENTION This invention relates to the lamination ofolefin polymers to various substrates with epoxy resins.

Olefin polymers are known to be useful in a large number of applicationssuch as in production of molded articles, films, fibers and the like. Inmany applications it would be highly desirable to be able to bond orlaminate such olefin polymers to various substrates including substratesof the same olefin polymers as well as substrates of other polymers andsubstrates of completely different materials such as metal, glass,paper, wood and the like. Unfortunately, as is taught in Handbook ofEpoxy Resins, Lee and Neville (1967) at pages 21-26, olefin polymers aregenerally chemically inert to adhesives. Thus the desirable strong bondsare not generally formed between olefin polymer and adhesive inlaminates of olefin polymers to different substrates.

It would therefore be highly desirable to provide a means for improvingthe bond strengthbetween olefin polymers and various substrates SUMMARYOF THE INVENTION The present invention is a method for bonding an olefinpolymer to a substrate which comprises the steps of surface sulfonatingthe olefin polymer and adhering the surface sulfonated olefin polymersto the substrate with epoxy resin.

The practice of the present invention is useful in the sealing of olefinpolymer containers; in laminating films or fibers of olefin polymers tofilms and/or fibers of like or different material suchas metal, glassand the like; in adhering articles of metals, plastics, paper, glass andthe like to olefin polymer articles, such as in the lamination ofmetallic spouts or inlet conduits to olefin polymer containers such astanks and drums and'the like; and in a wide variety of otherapplication.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS For the purpose ofthis invention an olefin polymer means sulfonatable homopolyrners andcopolymers of monomers containing an ethylenically unsaturated grouprepresented by the formula and chlorinated polypropylene as well asblends of the aforementioned polymers and copolymers. Especiallypreferred olefin polymers are the high density polyethylenes havingdensities in the range of from about 0.950 to about 0.978 and meltindexes in the range of from about 0.5 to about decigrams per minute[ASTM D-l238-65T(E)] and polypropylenes having densities in the range offrom about 0.900 to about 0.920 and melt flow viscosities in the rangeof from about 0.5 to about 15 decigrams/minutes [ASTM D- l238-65T(L)].Also advantageously employed are acras the conjugated aliphatic dienes,e.g., butadiene and isoprene, and polymers of monovinylidene aromaticcarbocyclic monomers such as styrene, t-butylstyrene, chlorostyrene andother substituted styrenes. Also included are polymers such aschlorinated polyethylene ylonitrile/butadiene/styrene terpolymers(so-called ABS resins) and polystyrene and impact polystyrene andstyrene polymers containing from about 5 to about 25 weight percent ofdiene rubber such as polybutadiene and styrene/butadiene copolymerrubber.

The olefin polymer in the form of film, fiber or any other shapedarticle including containers and covers therefor, bottles, tanks, pails,etc., can be sulfonated by contacting the surfacesthereof with vaporphase or liquid phase sulfonating agents. Preferably, vapor phasesulfonating agents are employed. If desired, only the surface of theolefin polymer to be bonded to the substrate (i.e., the mating surface),need be sulfonated. Such can be accomplished by masking the portions ofthe olefin polymer which are not to be sulfonated. Generally this is notworthwhile since the time and effort required to mask such portions ofthe olefin polymer exceed the value of the chemicals needed to sulfonatethe entire surface of the olefin polymer.

A preferred method of sulfonating the olefin polymers is to expose theolefin polymer to gaseous sulfur trioxide, preferably diluted with a dryinert gas such as air, nitrogen, helium, carbon dioxide, sulfur dioxideand the like. The concentration of sulfur trioxide in the gaseoussulfonating agent can vary from about 0.1 to I00 volume percent based ontotal gaseous sulfonating agent, preferably from about 2 to about 20volume percent of sulfur trioxide. The foregoing volume concentrationscorrespond to about 0.003 to about 3 grams of sulfur trioxide per liter(at atmospheric pressure) for the range of 0.1 to 100 volume percent andabout 0.06 to about 0.6 grams of sulfur trioxide per liter for the rangeof 2 to 20 volume percent. The time of sulfonation required to producean acceptable degree of sulfonation varies with the concentration ofsulfur trioxide and the temperature. For example, at room temperature(i.e.,-25C), 2 volume percent sulfur trioxide requires a time of 0.3 toseconds to provide acceptable degree of sulfonation. At temperature of35C, the time required when using 18 volume percent sulfur trioxide isshortened to about 0.1 to about 30 seconds. As evidenced by theforegoing, the time and concentration of sulfut trioxide are inverselyrelated, thus any combination of the above variables may be used to suitspecific. needs. It is important to exclude water vapor from the abovegases by a conventional drier tube since in the presence of water in aliquid or vapor form, the sulfur trioxide is converted to droplets ofsulfuric acid of varying concentration and uniform sulfonation of theplastic is either inhibited or prevented.

Another method of sulfonating the plastic substrates is to use a 10% byweight solution of sulfur trioxide in an inert liquid solvent, such as aliquid poly-chlorinated aliphatic hydrocarbon. Inert liquid solventscoming within the purview of this embodiment of the invention aremethylene chloride, carbon tetrachloride, perchloroethylene,sym-tetrachloroethane and ethylene dichloride. However, otherconcentrations may be used, for example, from about 1% to about 25%weight SO in an inert solvent. A dilute solution in the range of 1-10percent of weight with a contact time of thirty seconds to twentyminutes at room temperature (25C) is normally adequate to give thedesired degree of sulfonation, i.e., at least 0001 milligram of sulfurtrioxide equivalents in the form of sulfonic acid groups per squarecentimeter of polyolefin surface. To obtain a degree of sulfonation inthe preferred range of 0.005 to 5 milligrams of sulfur trioxideequivalents per square centimeter, it is desirable to employ generallyhigher temperatures and/or concentrations of sulfur trioxide in theaforementioned range.

It is therefore to be understood that in either vapor phase or liquidphase the time and concentration are inversely related so that if shortcontact times are desired, one must use a higher concentration.Oversulfonation is to be avoided since the sulfonation agents canblacken the polymer and severely corrode it. Generally, an amount ofsulfonation greater than 50 milligrams of sulfur trioxide equivalentsper square centimeter does not contribute much to the ultimate adhesionand is therefore uneconomical.

Examples of other liquid phase sulfonating agents are oleum,chlorosulfonic acid, and sulfuryl chloride dissolved in a suitable inertsolvent such as methylene chloride, carbon tetrachloride,perchloroethylene, tetrachloroethane, and ethylene dichloride. lt isnoted, however, that chlorosulfonic acid or sulfuryl chloride aregenerally more acceptable in treatment of aromatic olefin polymers suchas polystyrene than in treatment of aliphatic olefin polymers such aspolyethylene. [t is further understood that olefin polymers whichnormally dissolve in the aforementioned solvents are preferablysulfonated with sulfur trioxide in the gaseous phase as previouslydescribed.

While the foregoing methods are preferable, this invention is notlimited to enclosure members which are sulfonated by any particulartechnique. Therefore, any method of sulfonating plastic material whichwill give the hereinbefore specified degree of sulfonation is suitablefor the purpose of this invention.

Following the sulfonation step, the sulfonated olefin polymer can bewaterwashed, dried and coated with the epoxy resin. Alternatively thesulfonated olefin polymer can be neutralized with dilute aqueousammonia, ammonia gas or various amines such as methyl amine,isobutylamine, tetramethylene pentamine, monoethanolamine,triethanolamine, diethanolamine, aqueous solutions of salts ofhydroxides of alkali metals and alkaline earth metals, etc., prior tocoating with the epoxy resin.

The epoxy resins used in this invention can be any of the known epoxyresins as set forth in the book Handbook of Epoxy Resin" by Lee andNeville (1967), the preferred resins are liquid or flexible epoxy resinsderived from the reaction of bisphenol A and epichlorophydrin.Preferably, they range in epoxide equivalent weight from 170-250.Preferred resins have a range of viscosities from 500-90,000 centipoisesat 25C depending on the amount of reactive diluents that are added.Typical reactive diluents are butyl glycidyl ether and phenyl glycidylether.

In addition to the reactive diluents, it is sometimes desirable to addnonreactive modifiers or extenders such as dibutyl phthalate, pine oil,glycol ethers, and coal tar. Since coal tar has a high degree ofchemical resistance, it is the preferred modifier for use in epoxyresins in many applications.

The hardeners or curing agents used with the above epoxy resins toproduce the final cured resin are primary and secondary amines such asdiethylene triamine, triethylene tetramine, and tetraethylene pentamine;polyamides and the like. The amount of hardener to be used is usually anamount equal to the weight of the epoxy resin as is indicated in theabove Handbook of Epoxy Resins, Chapter 21.

The curing time for these epoxy resins and amine hardeners withmodifying agent is on the order of several days at 25C. However, thetime can be shortened to a great extent by heating. Thus, the sameresin/hardener formulation that takes 3 days to cure at 25C can be curedin l-2 hours at C.

For the purposes of this invention, the substrate to which the olefinpolymer is bonded is suitably composed of any material which forms asuitable bond with the epoxy resin as defined hereinbefore'The substratemay assume any solid form such as film, foil, fiber, sheet, plate,plaque, bowl, tub, or any other shaped article. lllustratively thematerial forming the substrate is glass; metal, such as steel, aluminum,copper, iron, zinc, lead, alloys thereof and the like; paper; wood;plastic and the like so long as it bonds well to epoxy resins. It isunderstood that, if the substrate comprises olefin polymer, it issurface sulfonated to the degree de' scribed hereinbefore.

The sulfonated olefin polymer is preferably adhered to the substrate by(1) applying epoxy resin to the locus of the seal, e.g., to thesulfonated olefin polymer or substrate or both, (2) placing thesulfonated olefin polymer in a contiguous relationship with thesubstrate such that the epoxy resin forms an interlayer between thesulfonated surface of the olefin polymer and the sub-v strate and (3)curing the epoxy resin for a time and at a temperature sufficient todevelop the desired maximum bond strength of the epoxy resin. Methodsand conditions for applying epoxy resins to substrates and curing theresins are well known to the art.

The following examples are presented to illustrate the present inventionand are not to be considered as a limitation on the scope of the claims.

EXAMPLE 1 A molded polypropylene automotive 12 volt battery case andcover with a peripheral groove are immersed in a 2 percent by weightsolution of sulfur trioxide in methylene chloride for 2 minutes at 25C.Both parts are removed and washed in a five percent by weight aqueousammonia solution and dried.

The groove .of the cover is then substantially filled with an epoxyformulation made from 98 parts of the diglycidyl ether of bisphenol-Ahaving 186-192 epoxide equivalent weight and a viscosity of 11,000-14,000 centipoises at 25C diluted with 2 parts butyl glycidylether. The final epoxy formulation is made by blending this with anequal weight portion of a 50 percent mixture of triethylene tetramineand coal tar containing a small amount of phenol to extend the settingtime.

The case and cover are then assembled, pressed together, and cured forseven hours at room temperature.

The final sealed battery is found to be liquid tight and structurallystrong.

EXAMPLE 2 In order to illustrate the superior strength of this method ofsealing containers, the following example is presented.

A. molded polypropylene battery cover having a peripheral groove isplaced halfway into a 2 percent by weight solution of sulfur trioxide inmethylene chloride for 1 minute at C so that a portion of the cover issulfonated in accordance with this invention and a portion is leftuntreated for comparison. The cover is removed and washed in a solutionof 5 percent by weight of aqueous ammonia and dried. Six test strips ofpolypropylene (Vs inch X l- /z inches X 6 inches) are then sulfonated ina similar manner and bonded into the peripheral groove of the sulfonatedhalf of the cover with the epoxy resin formulation of Example 1.

Six of the untreated polypropylene strips are bonded in the groove ofthe unsulfonated half of the cover with the epoxy resin formulation ofExample 1.

After curing the assembly for 6 hours at room temperature, the assemblyis clamped in an Instron testing machine, the strips are pulled and theforce in pounds is recorded as a function of time. The strips bonded tothe unsulfonated half of the cover failed in the range from 6-8 pounds.The strips bonded to the sulfonated half failed at 165 pounds while onestrip broke into two pieces at 90 pounds (no failure of the bond). Thistest thus shows the bonding of the cover was increased at least 20 timesby the sulfonation treatment and thus simulates an actual testing of thesealed battery under a rough handling test.

Improved results similar to the foregoing are ob tained using anon-grooved cover.

EXAMPLE 3 EXAMPLE 4 Six molded polyethylene cylindrical containers 3inches in diameter by 4 inches longhaving molded external screw threadson one end and-mating molded polyethylene caps having internal threadsare surface sulfonated by the method set forth in Example 1.

These containers are filled with calcium chloride and the external screwthreads are coated with a nonhardening epoxy formulation made from partsby weight of the diglycidyl ether of bisphenol A having an epoxyequivalent weight of 186-192, 40 parts by weight of the diglycidyletherof a mixture of polypropylene glycols having molecular weights in therange 610-670 with an epoxide equivalent weight of 305335 and 8.9 partsby weight of diethylene triamine. The containers are then sealed byscrewing on the cap.

The advantage of this flexible epoxy resin formulation is that it neverhardens and thus the screw cap can be secured and replaced several timeswith a good seal being obtained when it is screwed in place.

A similar set of unsulfonated containers are filled with the samedeliquescent chemical and sealed with the same epoxy formulation.

. When both sets of these containers. are stored in a humid atmosphere(90% relative humidity) for 24 hours, it is found that moisturepenetrates the seal of unsulfonated containers and cakes the calciumchloride whereas the sulfonated, sealed containers are completelyunaffected.

EXAMPLE 5 A series (Sample Nos. 1-8) of substrates of different polymersas indicated in Table I are surface treated at room temperature withsulfur trioxide in dry air using different concentrations and periods oftreatment as specified in Table l. The surface sulfonated substrates arecoated with epoxy resin* (*Reaction product of one part of diglycidylether of bisphenol-A with one part of a polyamide curing agent.) and arepressed together and held at ambient conditions for about one week. Thelaminated substrates are tested for bond strength by separating thesubstrates using a lap shear technique of Example 2. The results arereported in Table 1.

For purposes of comparison, a series (Sample Nos. A,-A.,) of untreatedsubstrates of the same polymers I are laminated with the epoxy resinused above and the laminated substrates are tested for bond strengthusing the lap shear technique. The results are recorded in Table l.

TABLE 1 Sulfonation Sulfonation Sample Conc., mole Treatment, Level, mg.Shear Stress at No. Substrate, Polymer percent Time, min. SO /cm.Failure, p.s.i.

1 HDPE/HDPE 10 0.75 0.019 335 2 HDPE/HDPE 10 3.0 0.070 413 A HDPE/HDPE 00 0 34 3 PP/PP [0 0.25 0.027 203 4 lP/PP 10 0.75 0.104 285 A-f lP/ll 0 00 27 5 ABS/ABS" 10 0.25 0.022 360 6 ABS/ABS" l0 [.0 0.044 430 AnABS/ABS" 0 0 0 230 7 HIPS/HIPS". 5 0.25 0.008 295 if: HIPS/HIPS 5 0.50.0[5 297 4 HIPS/HIPS 0 0 0 Not an example of the invention HDPE-Highdensity polyethylene having density of 0.967 and melt index of 8.0

dg./min.

PP- Polypropylene having density of 0.904 and melt flow of 2.0 dg./min.

ABS- Acrylonitrile/butadiene/styrene (17/8/75) terpolymer.

HIPS-High impact polystyrene containing 8 weight percent of poly(butadiene) rubber and 92 weight percent of polymerized styrene.

1 Lap Shear Technique of Example 2.

EXAMPLE 6 Two high density polyethylene gasoline tanks are treated onthe surfaces thereof at room temperature with mole percent of sulfurtrioxide in dry air for periods of H2 minute and 1 minute. The tanks arecoated about the opening thereof with epoxy resin* *Reaction product ofone part of diglycidyl ether of bisphenol-A with one part of polyamidecuring agent. and steel spouts having an external flange are pressedinto the opening of the gas tanks. The flange of each spout is matedwith the epoxy resin about the opening of the respective tank. Theresulting laminates are cured at ambient conditions for a period ofabout a week. The laminates are tested for bond failure and are found tofail as a result of substrate failure, i.e., destruction of thepolyethylene.

For purposes of comparison, an untreated polyethylene gasoline tank issimilarly coated with epoxy resin and mated with a similar steel spouthaving a flange. After curing under identical conditions, the resultinglaminate is tested for bond failure an is found to fail as result ofbond shear at much lower force than required to produce failure inforegoing samples.

What is claimed is:

l. A process for bonding an olefin polymer to a substrate whichcomprises (1 surface sulfonating the olefin polymer to a degree of about0.001 to about 50 milligrams of sulfur trioxide equivalents per squarecentimeter, (2) applying epoxy resin to the locus of the bond, (3)placing the sulfonated olefin polymer in a contiguous relationship withthe substrate such that the epoxy resin forms an inter layer between thesulfonated surface of the olefin polymer and the substrate and (4)curing the epoxy resin for a time and temperature sufficient to developthe maximum bond strength of the epoxy resin.

2. The process according to claim 1 wherein the olefin polymer ispolyethylene.

3. The process according to claim 1 wherein the olefin polymer ispolypropylene.

4. A process for bonding an olefin polymer to a metal which comprises(1) surface sulfonating the olefin polymer to a degree of about 0.001 toabout 50 milligrams of sulfur trioxide equivalents per squarecentimeter, (2) applying epoxy resin to the locus of the bond, (3)placing the sulfonated olefin polymer in a contiguous relationship withthe metal such that the epoxy resin forms an inter layer between thesulfonated surface of the olefin polymer and the metal and (4) curingthe epoxy resin for a time and temperature suffcient to develop themaximum bond strength of the epoxy resin.

5. A process for bonding an olefin polymer to glass which comprises (1)surface sulfonating the olefin polymer to a degree of about 0.001 toabout 50 milligrams of sulfur trioxide equivalents per squarecentimeter, (2) applying epoxy resin to the locus of the bond, (3)placing the sulfonated olefin polymer in a contiguous relationship withthe glass such that the epoxy resin forms an inter layer between thesulfonated surface of the olefin polymer and the glass and (4) curingthe epoxy resin for a time and temperature sufficient to develop themaximum bond strength of the epoxy resin.

6. A process for bonding an olefin polymer to paper which comprises (1)surface sulfonating the olefin polymer to a degreee of about 0.00] toabout 50 milligrams of sulfur trioxide equivalents per squarecentimeter, (2) applying epoxy resin to the locus of the bond, (3)placing the sulfonated olefin polymer in a contiguous relationship withthe paper such that the epoxy resin forms an inter layer between thesulfonated surface of the olefin polymer and the paper and (4) curingthe epoxy resin for a time and temperature sufficient to develop themaximum bond strength of the epoxy resin.

2. The process according to claim 1 wherein the olefin polymer ispolyethylene.
 3. The process according to claim 1 wherein the olefinpolymer is polypropylene.
 4. A process for bonding an olefin polymer toa metal which comprises (1) surface sulfonating the olefin polymer to adegree of about 0.001 to about 50 milligrams of sulfur trioxideequivalents per square centimeter, (2) applying epoxy resin to the locusof the bond, (3) placing the sulfonated olefin polymer in a contiguousrelationship with the metal such that the epoxy resin forms an interlayer between the sulfonated surface of the olefin polymer and the metaland (4) curing the epoxy resin for a time and temperature sufficient todevelop the maximum bond strength of the epoxy resin.
 5. A process forbonding an olefin polymer to glass which comprises (1) surfacesulfonating the olefin polymer to a degree of about 0.001 to about 50milligrams of sulfur trioxide equivalents per square centimeter, (2)applying epoxy resin to the locus of the bond, (3) placing thesulfonated olefin polymer in a contiguous relationship with the glasssuch that the epoxy resin forms an inter layer between the sulfonatedsurface of the olefin polymer and the glass and (4) curing the epoxyresin for a time and temperature sufficient to develop the maximum bondstrength of the epoxy resin.
 6. A process for bonding an olefin polymerto paper which comprises (1) surface sulfonating the olefin polymer to adegreee of about 0.001 to about 50 milligrams of sulfur trioxideequivalents per square centimeter, (2) applying epoxy resin to the locusof the bond, (3) placing the sulfonated olefin polymer in a contiguousrelationship with the paper such that the epoxy resin forms an interlayer between the sulfonated surface of the olefin polymer and the paperand (4) curing the epoxy resin for a time and temperature sufficient todevelop the maximum bond strength of the epoxy resin.